The objective of the present study was to investigate whether the injection of a tolerated
protein (indirect effects) affects the formation of
granulomas around Schistosoma mansoni eggs trapped in the lungs after intravenous (iv) injection into normal (noninfected) C57BL/6 mice (6 animals per group). To induce oral tolerance to chicken egg
ovalbumin a 1/5 dilution of egg white in water was offered ad libitum in a drinking bottle for 3 days. Control mice received water. After 7 days, control and experimental animals were injected iv with 2,000 S. mansoni eggs through a tail vein. In some mice of both groups the iv injection of eggs was immediately followed by intraperitoneal (ip) immunization with 10 micro g of dinitrophenylated conjugates of
ovalbumin (DNP-Ova) emulsified in complete
Freund's adjuvant (CFA) or only CFA; 18 days later, mice were bled and killed by
ether inhalation. The lungs were fixed in
formalin and embedded in
paraffin. Serial sections of 5 m were stained with Giemsa, Gomori's
silver reticulin and Sirius red (pH 10.2).
Granuloma diameters were measured in histological sections previously stained with Gomori's
reticulin. Anti-DNP and anti-soluble egg
antigen (SEA)
antibodies were analyzed by ELISA. In mice orally tolerant to
ovalbumin the concomitant ip injection of DNP-Ova resulted in significantly lower anti-SEA
antibodies (ELISA*: 1395 +/- 352 in non-tolerant and 462 +/- 146 in tolerant mice) and affected
granuloma formation around eggs, significantly decreasing
granuloma size (area: 22,260 +/- 2478 to 12,993 +/- 3242 m ). Active mechanisms triggered by injection of tolerated
antigen (
ovalbumin) reduce
granuloma formation.